Bird strikes to both military and civilian aircrafts represent a common threat to flight safety and have caused numerous unavoidable accidents leading to human casualties and higher rate of bird kills Most accidents occur when the bird hits the windscreen or flies into the engines. These accidents cause annual damages that have been estimated at $400 million within the United States alone and up to $1.2 billion to commercial aircrafts worldwide. Additionally, damages in and around the facilities and aircrafts where birds nest and congregate cost millions of dollars in the man-hours needed for bird strike prevention and clean-up.
Major accidents involving civil aircrafts are quite low and it has been estimated that there is only about 1 accident resulting in human death in one billion (109) flying hours. The majority of bird strikes (65%) cause little damage to the aircraft but result in a great number of bird fatalities.
The force of the impact on an aircraft depends on the weight of the animal and the speed difference and direction at the impact. The energy of the impact increases with the square of the speed difference. Hence, a low-speed impact of a small bird on a car windshield causes relatively little damage. High speed impact, as with jet aircraft, can cause considerable damage and even catastrophic failure to the vehicle. The energy of a 5 kg (11 lb) bird moving at a relative velocity of 275 km/h (171 mph) approximately equals the energy of a 100 kg (220 lb) weight dropped from a height of 15 meters (49 ft). The momentum of the bird in this case is considerably less than that of the ton weight, and, therefore, the force required to deflect it is also considerably less. However, according to the FAA, only 15% of strikes (ICAO 11%) actually result in damage to the aircraft.
Most often, bird strikes occur during takeoff or landing, or during low altitude flights. However, bird strikes have also been reported at high altitudes, some as high as 6,000 m (19,685 ft) to 9,000 m (29,528 ft) above the ground. Bar-headed geese have been seen flying as high as 10,175 m (33,383 ft) above sea level. An aircraft over the Côte d'Ivoire collided with a Rüppell's Vulture at an astonishing altitude of 11,300 m (37,073 ft), the current record avian height. Majority of bird collisions occur near or on airports (90%, according to the International Civil Aviation Organization (ICAO)) during takeoff, landing and associated phases. According to the FAA Wildlife Hazard Management Manual (2005), less than 8% of strikes occur above 900 m (2,953 ft) and 61% occur at less than 30 m (100 ft). The point of impact is usually any forward-facing edge of the vehicle such as a wing leading edge, nose cone, jet engine cowling or engine inlet.
Accordingly, there is a need for an avian denial system at airports and airfields that deny or repel birds access to critical areas of the airport and runways, particularly to areas around aircrafts and other high value systems, thereby avoiding or reducing potential property damage and possible loss of life. The domain of the action of the avian denial system must extend beyond the airfield or the airspace of the airport to provide safe passage of aircrafts during takeoff, landing, and during low altitude flights within and near the airspace. The avian denial system must be capable of preventing other forms of damage caused by birds nesting and perching in unwanted areas and assure collision avoidance between aircraft and birds with the highest probability possible during daily flight operations without impacting mission requirements.
Birds roosting or feeding in the vicinity of runways or flying in the airspace of the airport are often startled by an approaching aircraft and, in an attempt to escape, may be forced to take flight within the flight path of the aircraft and get sucked into a jet turbine. Jet engine ingestion is extremely serious due to the rotation speed of the engine fan and engine design. As the bird strikes a fan blade, that blade can be displaced into another blade and so forth, causing a cascading failure. Jet engines are particularly vulnerable during the takeoff phase when the engine is turning at a very high speed and the plane is at a low altitude where birds are more commonly found.
Accordingly, there is also a need for an active non-lethal avian denial system that will not injure, kill or affect the well-being of birds around airports and airfields. The system must be capable of detecting birds flying into an area where there is a potential for collision with an aircraft. For the system to be used by the U.S. military, the active non-lethal avian denial system should comply with the requirements necessary to manage the natural resources of each military reservation within the United States and to conserve migratory birds and their habitat. At the same time, the system must not interfere with any current operational aircraft or ground-based sensor systems and must not impact airport personnel or other people in the vicinity of the airport/aircraft.
There is a further need of a non-lethal avian denial system that is more capable than the current audio deterrent systems, which are only marginally effective and are further discussed in the Detailed Description section hereinbelow.